1. Field of the Invention
The present invention relates to a device for an electrophotographic apparatus and, more particularly, to a toner fixing device having a one piece frame supporting the fixing device's rollers.
2. Background Art
To transfer an image to a sheet of paper, the typical electrophotographic apparatus uses a photosensitive drum with a surface that becomes conductive when exposed to light. The drum is charged by a charging roll and then selectively exposed to light by an exposing unit. This creates an latent electrostatic image on the photosensitive drum. A developer then adds fine toner particles to the electrostatic image forming a latent toner image. The toner image is then transferred to a sheet of paper by a high pressure toner image transfer unit. The toner image is then fixed and melted onto the paper by a fixing device. The typical fixing device has a heating roller which fuses the toner image into the paper and a pressure roller for pressing the sheet against the heating roller. The heating roller is cylindrical and has a heating element, such as a halogen lamp, which keeps the heating roller at the necessary temperature to melt the toner particles into the paper. A typical temperature for the surface of the roller is somewhere around 150.degree. and 200.degree. C. The heating roller and the pressure roller rotate in the opposite direction so as to nip a piece of paper between the two rollers. After the image is fixed, the paper is discharged by a discharge roll unit to a collector tray.
The development of electrophotographic copiers has led to a corresponding development of many different types of fixing devices. Initially the ends of the rollers were supported by two piece frames, which led to a certain lack of dimensional precision. This led to the use of one piece frames in some fixing devices. For example, U.S. Pat. No. 4,965,640 to Watarai entitled Image Forming Apparatus Including Detachable Toner Fixing Unit, mentions a detachable heat and pressure fixing device that has the ends of both rollers supported by one piece frames. Another example of a removable heat and pressure fixing device using one piece frames to support the ends of its rollers is shown in U.S. Pat. No. 5,579,098 to Noguchi entitled Image Forming Apparatus with Removable Fixing Unit. U.S. Pat. No. 4,259,920 to Sasaki entitled Toner Image Pressure Fixing Device, shows a one piece frame which supports an end of two pressure rollers and has a spring located in a slot of the frame. Both U.S. Pat. No. 5,543,905 to Oda entitled Toner Fixing Device for Image Forming Apparatus and U.S. Pat. No. 4,812,873 to Inagaki entitled Heat Fixing Unit in an Electrophotographic Copying Apparatus, show a heat and pressure fixing device with one piece frames supporting the ends of the rollers.
I have observed that what is needed but so far unaddressed by the art is a heat and pressure fixing device that supports the ends of its roller with one piece frames, that has a spring located in a slot in each one piece frame for increasing the pressure between the rollers, and that is attachable to the electrophotographic apparatus using mounting brackets. I expect that such a fixing device will increase the dimensional accuracy of the fixing device and simplify the manufacturing process.